Process of coating



Patented Mar. 17, 1942 PROCESS F COATING .lolm S. Thompson, Detroit,Mich, assignor to harass Rust Proof (Jemuany, Detroit, Mich.

No Drawing. Application September 28, 1935, Serial No. 42,670. RenewedAugust 28, 1938 This invention relates to the field of the chemicalcoating of metals. An object of the invention is the rendering ofmetallic surfaces resistant to corrosion. A further object of theinven-- tion is to form on metallic surfaces a chemical coating whichresists corrosion when coated with a paint, lacquer, or enamel andprovides a base coat to which the applied coatings adhere in a muchfirmer manner than they would to the bare metal.

Generally speaking, the invention comprises the use of solutionscontaining soluble hydrofluosilicic compounds with the addition of anoxidizing agent with or without accelerating agents. Hydrofiuosillcicacid (HaSiFa) and soluble salts of this acid are comprised generally.oxidizing agents such as hydrogen peroxide may be employed andaccelerating agents such as nitrates may be used.

By the use of these materials surfaces of metals such as iron, steel,aluminum and zinc and alloys are rendered rust resistant and in manycases coatings are formed which serve as a rust resisting base forpaints, lacquers, enamels, and other coating compositions.

The process comprises generally treatment of the metal surface by any ofthe ordinary methods. .In the following examples which are given by wayof illustration and not limitation the metallic surfaces were immersedin the solutions at a boiling }.temperature. The usual processing timewas 5 minutes, although this may be decreased if desired. 'It isunderstood that the essential thing is to bring about a reaction betweenthe surface of the metal and the solution and that the time,temperature, and other factors of operation may be varied considerablywithout departing from the scope of the invention. In the followingexamples 2" x 4" panels were employed in the usual case.

Example 1.--A sheet of aluminum was immersed in a 200 cc. solution towhich had been added /2 gram chromic acid, 3 cc. HaSiFc. The metal wasremoved after 5 minutes at a boiling temperature and a hard, mediumgray, very uni- ?form coating had been produced upon the surface "of thealuminum. When the same ingredients are used with the addition of 2grams of sodium nit'rate, a brown coating is obtained which is liner.and softer.

Example 2.-The same conditions as in Example 1 were employed using asolution containing gram chromic acid and 5 grains manganesesilicofluoride. A medium gray. very uniform, medium hard coating wasobtained on the alumimm. when 2 grams of sodium nitrate is used with theother ingredients a harder, lighter, thinner coating is obtained.

Example 3.--Under the same conditions as in Example 1 a solution wasemployed containing V3 gram chromic acid, and 5 grams sodiumsilicofluoride. Th aluminum surface had a hard thin, light gray coating.When 2 grams of sodium nitrate is used with the other ingredients thesame result is obtained.

Example 4.Under the same conditions as in Example 1 an aluminum sheetwas treated with a solution containing 2 cc. of hydrogen peroxide and 3cc. hydrofiuosilicic acid. Coatings were obtained which may be describedas white, under a fairly hard gray surface. When 2 grams of sodiumnitrate is employed with the other ingredients a medium gray, fairlyhard coating is obtained.

Example 5.--Under the same conditions as in mample 1 an aluminum objectis immersed in a solution to which has been added 1 gram potasslumpermanganate and 3 cc. hydrofluosilicic acid.

A red-purple iridescent fairly hard coating is obtained. When 2 grams ofsodium nitrate is used with the same ingredients 8 dark purple, soft anddusty coating is obtained.

Example 6.-Under the same conditions as in the preceding examples asolution was employed using 2 grams potassium dichromate and 5 cc. hy-

drofluosilicic acid. A rather soft gray coating is obtained on thealuminum. When 2 grams of sodium nitrate is used with the otheringredients 9. hard, brown coating is obtained.

Example 7.-Under the same conditions as in the preceding examples asolution is used containing 2 grams sodium chromate with 3 cc.hydrofluosiiicic acid. A dark gray, hard coating is obtained on thealuminum surface. When 2 grams of sodium nitrate is used together withthe other ingredients a light brown, hard, thin coating is obtained.

Example 8.-Under the same conditions an aluminum surface is treated witha solution containing 2'grams chromium sulphat and 3 cc. hy-'drofluosilicic acid. There is obtained on the aluminum surface a softgreen gray coating over a hard thin white. When 2 grams sodium nitrateis used together with the other ingredients, a thin,"

2 was taken. There was obtained on a steel surface a dark, gray, fairlyhard coating.

Example lib-The solution employed was made up by adding 1 gram chromicacid, 2% cc. Basil;

and 2 grams sodium nitrate. A black, adherent coating .was obtainedunder a brown dust on a steel surface in 5 minutes.

Example 11.Under the same conditions as in the preceding examples asteel object was processed in a solution containing 2 grams chromlcacid, 5 grams manganese silicofluoride, 2% grams sodium nitrate for 1 to5 minutes. There was obtained a black, adherent coating. The sameresults were obtained with the following ingredients in solution:

2 grams CrOa plus 5 gramsFeSiFa plus 2% grams N'aNOa 2 gr. Cr05+5 gr.FeSiFe+2 gr. MniNOa):

2 gr. Cra+3 cc. Fea(SiFs)s+2 gr. NaNO:

10 cc. H2SiFc+4 gr. KzCr0+2 gr. mason:

cc. HaSiFe+2 gr. KaCnO1+2 gr. ammo:

2 gr. Cr:(SO4)a+5 cc. HaSiFs+2 gr. NaNOl Example 12.--Under the sameconditions as in the preceding examples a steel object was proc-' essedin a solution containing 1 cc. HsSiFs+3 gr. K1804 for 5 minutes. vA likesolution with 2 gr. NaNO: added gave the same rust proofing results astested in the salt spray, both being an improvement over non-treated.steel.

Example 13.-Other salts that may be substituted for K2804 in thecombinations given in the example Just above are:

NaCl NaaSOs NaHzPOs NaHaPOs NMMOOQ KClO: NMWOs N82340:

HCl HNO:

HsPO4 H280:

HsPOa H010:

HClQ4 Boric acid Molybdio acid Tungstic acid Slight variations inproportions may be necessary in the chemicals used in these examples,but added corrosion resistance is. obtained from all of them.

Example 16.-Under the same conditions as in the preceding examples asteel object was processed in a solution containing 2 co.HaSiFs+l cc.

30% H202. A soft brown and black coating re sulted in 5 minutes. Alikesolution containing 1 cc. HzSiFs+1 cc. 30% H202+2 gr. NaNO: produced avery uniform, adherent, light gray coating in 5 minutes. Both of thesetreatments gave exceptionally good salt spray test results.

Example 17.Under the same conditions as in the preceding examples asteel object was processed in a solution containing 2 cc. HaSiFs andsuited in 5 minutes which was adherent under a loose top dust.

Example 18.Underthe same conditions as in the preceding examples a steelobject was processed in a solution containing 1 cc. HaSiFs+2 gr. KaSzOa.A thin-iridescent coating resulted in 5 minutes but the addition of 2grams NaNOl to this solution produced a dark gray coating.

Example 19.Under the same conditions as the preceding examples a steelobject was processed in a solution containing 6 gr. NaIhPO4+6 gr.MnSiFs+4 gr. Mn(NO:)z and a gray adherent coating resulted in 15 minutesat boiling temperature. Manganese dihydrogen phosphate may besubstituted for the sodium phosphate in this example and FeSiFs orZllSiFs may be substituted for the MnSiF'o.

Example 20..Under the same conditions as in the preceding examples asteel object was processed in a solution containing 2 /2 cc. HzSiFs and2 gr. NaNOs. A very uniform soft gray coating resulted in 5 minutes. 5gr. MllSiFs may be substituted for the H1811"; in this combination andvery good corrosion resistance is shown from both treatments.

Example 21.-A 200 cc. solution containing 5 gr. MnSiFa+.2 cc. 85% 8.1904produced a good coating in 5 minutes. The addition of 2 grams NaNOl tothis solution also produced a resistant 1 gr. KMnOa A gray and browncoating recoating in 5 minutes. In this example FeSiFs may besubstituted for MnSiFs and Mn(NOa)z may be substituted for the NaNOa.

In thefollowing examples objects with a zinc surface were immersed in aboiling solution for 5 minutes.

Example 22.-1 gram CrO: plus 2 cc. HzSiFs.

A thin gray, fairly hard coating was obtained. When 2 grams of sodiumnitrate is used with the other ingredients a coating is obtained whichis gray with green tint, fairly hard and uniform. In this example ifsodium nitrate is replaced by manganese nitrate or zinc nitrate similarresults are obtained. When aluminum nitrate is employed in place of thesodium nitrate a coating is obtained which is hard, adherent and heavygray.

Example 23.-2 grams chromium sulphate plus 2 cc. HzSiFs. When 2 grams ofsodium nitrate is used with the other ingredients a uniform, dark, dull,hard, adherent coating was obtained.

Example 24.1 gram CrO: plus 1 gram KMnOr plus 2 cc. HaSiFa. A hard graycoating under a soft purple one is obtained. When 2 grams of sodiumnitrate is used with the other ingredients similar results are obtained.

Example 25.1 gram CrO: plus 5 grams MnSiFs, A coating is obtainedsimilar to that when using HaSiFs in place of MIlSiFs. When 2 gramssodium nitrate is employed with the other ingredients a green coating isobtained.

Example 26.--2 cc. HaSiFs plus 2 grams sodium nitrate. A transparent,fairly hard, dark gray coating is obtained. When zinc nitrate is .usedin place of sodium nitrate, similar results are obtained. Example 27.--1gram chromic acid plus 1 gram of K2820: plus 1 cc. mSiFa. A hard graymixed dark and light coating is obtained. When 2 grams sodium nitrateare'used with the other ingredients a soft, dark green shiny finish isobtained. 1

In the above examples metals other than those specifically mentioned canbe processed. Time, temperatures, proportions and ingredients can bevaried well within the scope of the invention, the essence being thetreatment of metals with solutions containing the SiFc radical togetherwith the use of oxidizing agents with or without accelerating agents.

The examples mentioned above include hydrogen-peroxide, nitric acid andnitrates, chromic acid, chromates and dichromates, permanganates,sulphurous acid and sulphites, chloric and perchloric acids andchlorates, molybdates, tungstates, and persulphates, which arerecognized oxidizing agents, and other compatible oxidizing agents maybe used. The oxidizing agent must, of course, be a compatible material,that is, it must be soluble in the solution and its oxidizing power mustnot be destroyed by the other ingredients in the solution before it hasan opportunity to exert its oxidizing power in the chemical reactionthat takes place at the surface of the work.

It has been found that acceleration is gained by adding to thesesolutions a soluble salt of a metal below the respective metal beingtreated in the electromotive series. This acceleration is apparent inquickening of processing time, more uniformity in the coating and inproducing aheavier coating. In the case of treating an iron surface,salts of metals slightly above iron in the electromotive series may beused.

What I claim is:

1. A process of treating a surface of a metal included in the groupconsisting of iron, steel, zinc, aluminum and their alloys, whichcomprises subjecting said surfaces to the action of a heated solutioncontaining the SiFe radical and one of the group consisting of chromicacid and nitric acid, and treating the metallic surface until a visibleprotective paint-holding coating is obtained thereon and then applying acoating of one of the group consisting of paints, lacquers and enamels.

2. A process'of treating a surface of a metal included in the groupconsisting of iron, steel, zinc,'aluminum and their alloys, whichcomprises subjecting said surfaces to the action of a heated solutioncontaining a soluble hexavalent chromium compound and one of the groupof HzSiFs and soluble salts thereof, at least one of the aforesaid beingadded in the form of acid and continuing such action until a visibleprotective paint-holding coating is obtained upon the metallie surfaceand thereafter applying a coating of one of the group consisting ofpaints, lacquers and enamels.

3. A process of treating a surface of a metal included in the groupconsisting of iron, steel, zinc, aluminum and their alloys, whichcomprises subjecting said surfaces to the action 'of a heated solutioncontaining chromic acid and one of the group of HzSiFa and soluble saltsthereof, and continuing such action until a visible protectivepaint-holding coating is obtained upon the metallic surface andthereafter applying a coating of one of the group consisting of paints,lacquers and enamels.

4. A process which comprises treating a surface of a metal included inthe group consisting of iron, steel, zinc, aluminum and their alloyswith a heated solution containing the radical SiFc and nitric acid, andcontinuing such treatment until a visible, protective paint-holdingcoating is obtained upon the metallic surface and thereafter coating thesurface with one of the group consisting of paints, lacquers andenamels.

5- A process of treating a surface of.a metal included in the groupconsisting of iron, steel,

zinc, aluminum and their alloys, which comprises subjecting saidsurfaces to the action of an aciduated heated solution containing as itschief active ingredients the SiFs radical and a compatible oxidizingagent, and treating the metallic surface until a visible protectivepaint-holding coating is obtained and thereafter applying to the metalsurfacea coating of one of the group consisting of paints, lacquers andenamels.

6. A process of treating a surface of a metal included in the groupconsisting of iron, steel, zinc, aluminum and their alloys, whichcomprises subjecting said surfaces to the action of an acidulated heatedsolution containing as its chief active ingredients the SiFs radical anda compatible oxidizing agent of the group consisting paints, lacquersand enamels.

JOHN S. THOMPSON.

